The GALAH Survey: Scientific Motivation

TL;DR

The GALAH survey aims to map the Milky Way's formation history by obtaining high-resolution spectra of a million stars to identify dispersed stellar remnants through their unique chemical signatures.

Contribution

This paper introduces the GALAH survey's scientific goals, methodology, and initial performance results of the HERMES spectrograph for large-scale chemical tagging.

Findings

HERMES achieved successful first-light performance.

Spectra contain 29 elemental absorption lines for chemical tagging.

Survey plans to analyze spectra of one million stars.

Abstract

The GALAH survey is a large high-resolution spectroscopic survey using the newly commissioned HERMES spectrograph on the Anglo-Australian Telescope. The HERMES spectrograph provides high-resolution (R ~28,000) spectra in four passbands for 392 stars simultaneously over a 2 degree field of view. The goal of the survey is to unravel the formation and evolutionary history of the Milky Way, using fossil remnants of ancient star formation events which have been disrupted and are now dispersed throughout the Galaxy. Chemical tagging seeks to identify such dispersed remnants solely from their common and unique chemical signatures; these groups are unidentifiable from their spatial, photometric or kinematic properties. To carry out chemical tagging, the GALAH survey will acquire spectra for a million stars down to V~14. The HERMES spectra of FGK stars contain absorption lines from 29 elements including light proton-capture elements, alpha-elements, odd-Z elements, iron-peak elements and n-capture elements from the light and heavy s-process and the r-process. This paper describes the motivation and planned execution of the GALAH survey, and presents some results on the first-light performance of HERMES.